1. Field of the Invention
The present invention relates to an armature for a rotating electric machine and a manufacturing method for the armature.
2. Description of Related Art
U.S. Pat. No. 5,508,577 (JP-A-7-231618) proposes an improved type armature coil structure for a rotating electric machine. This armature coil comprises outer coil elements and inner coil elements, which are assembled in an armature core and are joined to each other electrically and mechanically at the end protrusions thereof. Further, U.S. Pat. No. 5,778,512 (JP-A-9-182337) proposes to join the end protrusions of the outer and inner coil elements by arc welding method.
However, the arc welding is likely to cause an undesired joined part between the end protrusions of the outer and lower coil elements, because the outer coil element has a larger thermal capacitance than the inner coil element. That is, the end protrusion of the inner coil element tend to melt earlier than that of the outer coil element, when the welding arc is applied to the inner coil element first. The end protrusion of the inner coil element may, in the worst instance, melt and separate from the inner coil element before joined to the end protrusion of the outer coil element. Even in the case in which the welding arc is directed to the end protrusion of the outer coil element first, the welding arc tend to swing to either the outer or inner coil element because of a contact between the two end protrusions.
Further, the joined part produced between the end protrusions by the arc welding expands outwardly in its radial direction. The centrifugal force exerted to the expanded joined part becomes excessive. The arc welding also causes the crystal grains in the joined part to become coarse. Thus, it becomes hard to ensure mechanical strength (anti-fatigue strength) of the joined part against the centrifugal force.
As an alternative to the arc welding, a TIG-brazing may be used. However, the TIG-brazing necessitates additional steps to provide brazing materials sized in correspondence with the end protrusions to be brazed, and to insert or mount the brazing materials between or on the end protrusions to be brazed.